White mineral oils, also called white oils, are colorless, transparent, oily liquids obtained by the refining of crude petroleum feedstocks. In the production of white oils, an appropriate petroleum feedstock is refined to eliminate, as completely as possible, oxygen, nitrogen, and sulfur compounds, reactive hydrocarbons including aromatics, and any other impurity which would prevent use of the resulting white oil in the pharmaceutical or food industry. White oils generally fall into two classes, technical grade and medicinal grade. Technical grade white oils are those suitable for use in cosmetics, textile lubrication, bases for insecticides, and the like. The more highly refined medicinal grade white oils are those suitable for use in drug compositions, foods, and for the lubrication of food handling machinery. The medicinal grade white oils must be chemically inert and substantially without color, odor, or taste. Also, for these applications manufacturers must remove “readily carbonizable substances” (RCS) from the white oil. RCS are impurities that cause the white oil to change color when treated with strong acid. The Food and Drug Administration (FDA) and white oil manufacturers have stringent standards with respect to RCS, which must be met before the white oil can be marketed for use in food or medicinal applications. In particular, the. Code of Federal Regulations, 21 C.F.R. §172.878(1988) defines white mineral oil as a mixture of liquid hydrocarbons, essentially paraffinic in nature obtained from petroleum and refined to meet the test requirements of the United States Pharmacopoeia XX, pp. 532 (1980) for readily carbonizable substances and for sulfur compounds. The Ultraviolet Absorption Test generally measures the ultraviolet absorbance of an extract in the range of 260-350 nm, which absorbance is then compared with that of a naphthalene standard. This test sets forth limits for the presence of polynuclear compound impurities in the white oil.
White oil must also pass the Hot Acid Carbonizable Substances Test (ASTM D-565) to conform to the standard of quality required for pharmaceutical use. In order to pass this test the oil layer must show no change in color and the acid level is not darker than that of the reference standard colorimetric solution. From this test it will be seen that for purposes of interpreting test results, the art has recognized that a value of 16 or below on a standard test, the Hellige Amber C Color Wheel, is sufficient to pass the carbonizable substances test.
Medicinal grade white oils have a Saybolt color by ASTM D156-02 greater than +20 and have a low UV absorbance as defined in 21 CFR 178.3620. Medicinal white oils must also meet the requirements of 21 CFR 172.878.
Medicinal white oils are high value oils but are expensive to produce since they require a number of process steps which may include hydrocracking, hydrotreating, hydrofinishing and treating by an adsorbent or a solvent. An example of four stage catalytic process to make pharmaceutical white oils is U.S. Pat. No. 6,723,229. US published application 20060016724 relates to a process for producing white oils using a selective hydroisomerization catalyst.
There is an incentive to produce oils which meet medicinal white oil specifications at lower processing cost. What is desired are catalytic processes that produce medicinal white oils with minimal manufacturing costs and produce a separate medicinal white oil product not contaminated with other products including other grades of white oils.